Elastic wave resonators and filters

ABSTRACT

An elastic wave resonator including a pair of comb-shaped electrodes and a pair of reflector electrodes formed on a piezoelectric substrate. In one example, the pair of comb-shaped electrodes includes first and second overlapping regions in which electrode fingers of the comb-shaped electrodes interdigitate, the second overlapping region being provided on both outside edges of the first overlapping region in an overlapping width direction, an overlapping width of the first overlapping region being greater than an overlapping width of the second overlapping region, the pair of comb-shaped electrodes being configured to excite a first elastic wave in the first overlapping region and to excite a second elastic wave in the second overlapping region, a frequency of the first elastic wave being higher than a frequency of the second elastic wave.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation and claims the benefit under 35U.S.C. §120 of co-pending U.S. application Ser. No. 14/680,486 filed onApr. 7, 2015, which claims the benefit under 35 U.S.C. §119(a) and PCTArticle 8 to co-pending Japanese Patent Application No. 2014-079111filed on Apr. 8, 2014, all of which are hereby incorporated by referenceherein in their entireties for all purposes.

FIELD OF INVENTION

Aspects and embodiments relate generally to an elastic wave resonator,and an elastic wave filter, an antenna duplexer, a module, and acommunication device using the same.

BACKGROUND

An elastic wave device implemented using a 42 degree-rotated Y-cutlithium tantalate piezoelectric substrate has been commonly used for afilter and an antenna duplexer of a communication device. The elasticwave device is configured to use a plurality of comb-shaped electrodes(also referred to as interdigital transducer (IDT) electrodes) formed onthe piezoelectric substrate. Recently, there has been a need for anelastic wave device having higher performance and better temperaturecharacteristics. One approach to realizing such an elastic wave deviceinvolves making the piezoelectric substrate of lithium niobate andproviding a silicon oxide film on the IDT electrode so that thetemperature characteristic can be improved. This was expected to providea higher Q at resonance, especially in an elastic wave device usinglithium niobate that has a cut angle for the primary elastic wave to bea Rayleigh wave. However, spuriousness such as a spurious response inthe transverse mode, and a spurious response due to an undesired waveother than the Rayleigh wave as the primary elastic wave can be causedby a plurality of factors in such an elastic wave device. Thisspuriousness can degrade the filtering characteristics of the elasticwave device.

FIG. 19 illustrates an example of the configuration of a conventionalelastic wave resonator. In the example illustrated in FIG. 19, theelastic wave resonator has comb-shaped electrodes 1902 and reflectorelectrodes 1903 that are formed on a piezoelectric substrate 1901. Thisconfiguration experiences problematic spuriousness in the transversemode, particularly when the piezoelectric substrate of the elastic waveresonator is made of lithium niobate.

A conventional approach to solving the spuriousness problem in elasticwave resonators such as that shown in FIG. 19 includes using apodizationin the elastic wave resonator. For example, FIG. 20 illustrates aconfiguration of a conventional elastic wave resonator includingapodization. In the example shown in FIG. 20, the elastic wave resonatorhas comb-shaped electrodes 2002 and reflector electrodes 2003 that areformed on a piezoelectric substrate 2001. Here, the comb-shapedelectrode 2002 has apodization to suppress spuriousness in thetransverse mode, as described, for example, in US patent applicationpublication No. 2011/0068655.

SUMMARY OF INVENTION

Conventional elastic wave resonators, such as that shown in FIG. 20, forexample, suffer from degraded characteristics caused by a Q-valuedegradation due to the apodization, and further may be of an undesirablylarge size when the apodization is used. Still further, when the elasticwave resonator is used as an elastic wave filter, the elastic wavefilter may suffer from degraded insertion loss and degraded attenuationcharacteristics.

Accordingly, aspects and embodiments are directed to a relativelysmaller (downsized) elastic wave resonator having less spuriousness inthe transverse mode and improved characteristics. Additional aspects andembodiments are directed to providing an elastic wave filter and anantenna duplexer using such an elastic wave resonator, as well as amodule and a communication device using the same.

One embodiment is directed to an elastic wave resonator including apiezoelectric substrate and a comb-shaped electrode provided on an uppersurface of the substrate, the comb-shaped electrode including a firstoverlapping region and a second overlapping region, the secondoverlapping region being provided on the outside of the firstoverlapping region in an overlapping width direction, an overlappingwidth of the first overlapping region being greater than an overlappingwidth of the second overlapping region, and an electrode finger pitch inthe second overlapping region being greater than an electrode fingerpitch in the first overlapping region. According to this configuration,an elastic wave resonator having improved characteristics, includingless spuriousness, may be advantageously realized.

Various embodiments of the elastic wave filter may include any one ormore of the following features.

In one example, the elastic wave filter is configured such that afrequency of an elastic wave excited in the second overlapping region isless than a frequency of an elastic wave excited in the firstoverlapping region.

In another example, electrode fingers in the first overlapping regionand electrode fingers in the second overlapping region are connected viafirst connection electrode fingers, the first connection electrodefingers being configured to obliquely extend with respect to a directionin which the electrode fingers extend in the first overlapping region.

The elastic wave resonator may further include a dummy region in whichthe electrode fingers do not overlap with each other. In one example,the electrode fingers in the first overlapping region and the electrodefingers the second overlapping region are connected via first connectionelectrode fingers provided in a first connection region. The electrodefingers in the second overlapping region and the electrode fingers inthe dummy region can be connected via second connection electrodefingers provided in a second connection region. In one example, thefirst connection electrode fingers and the second connection electrodefingers obliquely extend with respect to a first direction in which theelectrode fingers extend in the first overlapping region, and the firstdirection is opposite to a second direction in which the secondconnection electrode fingers extend. In another example, the dummyregion has an electrode finger pitch greater than the electrode fingerpitch in the first overlapping region. The electrode fingers of thecomb-shaped electrode can be connected to a busbar electrode, apropagation direction length of which is greater than a propagationdirection length of the first overlapping region.

In another example, a width of electrode fingers in the secondoverlapping region is greater than a width of electrode fingers in thefirst overlapping region.

In another example, the first overlapping region includes a first numberof electrode fingers, and the second overlapping region includes asecond number of electrode fingers, fewer than the first number ofelectrode fingers.

In another example, the second overlapping region includes a first phaseregion and a second phase region, a phase of an elastic wave generatedby the electrode fingers of the first phase region being different froma phase of an elastic wave generated by the electrode fingers of thesecond phase region.

According to any of the above configurations, an elastic wave resonatorhaving improved characteristics, including less spuriousness, can beadvantageously realized.

The elastic wave resonator may further include a thin dielectric filmmade of SiO₂ disposed over the comb-shaped electrode. According to thisconfiguration, an elastic wave resonator having an improved and bettertemperature characteristic can be advantageously realized.

In one example, the piezoelectric substrate is made of lithium niobateand has a cut angle ranging from 120 degrees to 135 degrees in Y-cut.According to this configuration, an elastic wave resonator havingimproved characteristics, including less spuriousness, when the primaryelastic wave is Rayleigh wave can be advantageously realized.

Another embodiment is directed to an elastic wave filter including aplurality of elastic wave resonators, at least one of the elastic waveresonators being an elastic wave resonator according to any one of theabove-discussed embodiments, examples, or configurations. Accordingly,an elastic wave filter having an improved characteristic can berealized.

Another embodiment is directed to a longitudinal-mode elastic wavefilter including a plurality of elastic wave resonators disposedadjacent to one other in a propagation direction of an elastic wave inthe elastic wave filter, at least one of the elastic wave resonatorsbeing an elastic wave resonator according to any one of theabove-discussed embodiments, examples, or configurations. Accordingly,an elastic wave filter having an improved characteristic can beadvantageously realized.

According to another embodiment, an antenna duplexer includes atransmission filter and a reception filter, at least one of thetransmission filter and the reception filter being an elastic wavefilter according to any of the above-discussed embodiments. According tothis embodiment, an antenna duplexer having an improved characteristiccan be advantageously realized.

Another embodiment is directed to a module including an elastic wavefilter or antenna duplexer according to any of the above-discussedembodiments. According to this embodiment, a module having an improvedcharacteristic can be advantageously realized.

Another embodiment is directed to a communication device including anelastic wave filter or antenna duplexer according to any of theabove-discussed embodiments. According to this embodiment, acommunication device having an improved characteristic can beadvantageously realized.

According to another embodiment, an elastic wave filter comprises apiezoelectric substrate and a plurality elastic wave resonators disposedon an upper surface of the piezoelectric substrate, each elastic waveresonator including a comb-shaped electrode having a first overlappingregion and a second overlapping region, the second overlapping regionbeing provided on outside edges of the first overlapping region in anoverlapping width direction, an overlapping width of the firstoverlapping region being greater than an overlapping width of the secondoverlapping region, and an electrode finger pitch in the secondoverlapping region being greater than an electrode finger pitch in thefirst overlapping region.

As described above, embodiments of the elastic wave resonator inaccordance with the present invention can achieve the effect ofrealizing a downsized elastic wave resonator having less spuriousness inthe transverse mode and improved characteristics. Further, configuringan elastic wave filter and an antenna duplexer to use such an elasticwave resonator can achieve the effect of realizing a downsized elasticwave filter and antenna duplexer having improved characteristics. Stillfurther, configuring a module and a communication device to use such anelastic wave filter and an antenna duplexer can achieve the effect ofrealizing a downsized module and communication device having improvedcharacteristics.

Still other aspects, embodiments, and advantages of these exemplaryaspects and embodiments are discussed in detail below. Embodimentsdisclosed herein may be combined with other embodiments in any mannerconsistent with at least one of the principles disclosed herein, andreferences to “an embodiment,” “some embodiments,” “an alternateembodiment,” “various embodiments,” “one embodiment” or the like are notnecessarily mutually exclusive and are intended to indicate that aparticular feature, structure, or characteristic described may beincluded in at least one embodiment. The appearances of such termsherein are not necessarily all referring to the same embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

Various aspects of at least one embodiment are discussed below withreference to the accompanying figures, which are not intended to bedrawn to scale. The figures are included to provide illustration and afurther understanding of the various aspects and embodiments, and areincorporated in and constitute a part of this specification, but are notintended as a definition of the limits of the invention. In the figures,each identical or nearly identical component that is illustrated invarious figures is represented by a like numeral. For purposes ofclarity, not every component may be labeled in every figure. In thefigures:

FIG. 1 is a diagram illustrating one example of an elastic waveresonator according to one embodiment;

FIG. 2 is a transmission characteristic diagram corresponding to anexample of the elastic wave resonator of FIG. 1;

FIG. 3 is a transmission characteristic diagram according to theconventional elastic wave resonator of FIG. 19;

FIG. 4 is a diagram illustrating another configuration of an example ofthe elastic wave resonator of FIG. 1;

FIG. 5 is a diagram illustrating another configuration of an example ofthe elastic wave resonator of FIG. 1;

FIG. 6 is a diagram illustrating one example of comb-shaped electrodesfor one embodiment of the elastic wave resonator of FIG. 1;

FIG. 7 is a diagram illustrating another example of comb-shapedelectrodes for another embodiment of the elastic wave resonator of FIG.1;

FIG. 8 is a diagram illustrating one example of an elastic waveresonator according to another embodiment;

FIG. 9 is a transmission characteristic diagram corresponding to anexample of the elastic wave resonator of FIG. 8;

FIG. 10 is a transmission characteristic diagram according to aconventional elastic wave resonator;

FIG. 11 is a cross-sectional view of the elastic wave resonator of FIG.8;

FIG. 12 is a transmission characteristic diagram corresponding to oneexample of the elastic wave resonator of FIG. 11;

FIG. 13 is a transmission characteristic diagram according to aconventional elastic wave resonator;

FIG. 14 is a diagram illustrating another configuration of an example ofthe elastic wave resonator of FIG. 8;

FIG. 15 is a diagram of an elastic wave filter including examples of theelastic wave resonator according to FIG. 1 and/or FIG. 8;

FIG. 16 is a block diagram of one example of an antenna duplexerincluding the elastic wave filter of FIG. 15, according to certainembodiments;

FIG. 17 is a block diagram of one example of a module incorporating theelastic wave filter of FIG. 15, according to certain embodiments;

FIG. 18 is a block diagram of one example of a wireless communicationsdevice incorporating the antenna duplexer of FIG. 16, according tocertain embodiments;

FIG. 19 is a diagram illustrating one configuration of a conventionalelastic wave resonator; and

FIG. 20 is a diagram illustrating another configuration of aconventional elastic wave resonator.

DETAILED DESCRIPTION

Various aspects and embodiments of the present invention are describedbelow with reference to the drawings.

Referring to FIG. 1, there is illustrated one example of an elastic waveresonator 100 according to one embodiment. In the example illustrated inFIG. 1, the elastic wave resonator includes comb-shaped electrodes 102and reflector electrodes 103 that are formed on a piezoelectricsubstrate 101. The elastic wave resonator 100 is configured with anoverlapping portion between the comb-shaped electrodes 102 to excite anelastic wave, the overlapping portion including a first overlappingregion 104 and second overlapping regions 105. The second overlappingregions 105 are provided on both outside edges of the first overlappingregion 104, as shown in FIG. 1. The electrode fingers of the firstoverlapping region 104 and the electrode fingers of the secondoverlapping regions 105 are connected via first connection electrodefingers 106. The first connection electrode fingers 106 are provided infirst connection regions, each of which is located between the firstoverlapping region 104 and the second overlapping region 105. Further,the electrode fingers of the second overlapping region 105 and theelectrode fingers of a dummy region 107 are connected via secondconnection electrode fingers 108. The second connection electrodefingers 108 are provided in second connection regions, each of which islocated between the second overlapping region 105 and the busbarelectrode 110. As used herein, the dummy region 107 refers to a regionwhere the electrode fingers do not overlap with each other between thecomb-shaped electrodes 102. In the example illustrated in FIG. 1, thefirst connection electrode fingers 106 and the second connectionelectrode fingers 108 are connected in a direction oblique with respectto the direction in which the electrode fingers of the comb-shapedelectrode 102 extend. Further, the direction in which the firstconnection electrode fingers 106 extend is opposite to the direction inwhich the second connection electrode fingers 108 extend. As a result,the electrode fingers of the first overlapping region 104 are arrangedcollinear with the electrode fingers of the dummy region 107.

The first overlapping region 104 is a primary portion for exciting anelastic wave to obtain desired frequency characteristics. In oneexample, the overlapping width (W) of the first overlapping region 104is greater than the overlapping width of the second overlapping region105. Additionally, the electrode finger pitch of the second overlappingregion 105 may be greater than the electrode finger pitch of the firstoverlapping region 104, and as a result, the frequency of an elasticwave excited in the second overlapping region 105 may be lower than thefrequency of an elastic wave excited in the first overlapping region104. As used herein, the electrode finger pitch refers to the distancebetween the centers of adjacent electrode fingers.

FIG. 2 illustrates a transmission characteristic for the elastic waveresonator of FIG. 1. For comparison, FIG. 3 illustrates a transmissioncharacteristic for the conventional elastic wave resonator of FIG. 19.In the example of the elastic wave resonator 100 corresponding to FIG.2, a 128-degree LiNbO₃ substrate is used for the piezoelectric substrateso that the primary elastic wave can be a Rayleigh wave. In thisexample, the electrode finger pitch of the first overlapping region 104is 2.00 μm, and the electrode finger pitch of the second overlappingregion 105 is 2.02 μm. Additionally, the number of electrode fingers ofthe comb-shaped electrode 102 is one hundred (100), and the number ofthe electrode fingers of the reflector 103 is thirty (30). Furthermore,in this example, the metallization ratio of the electrode fingers of thesecond overlapping region 105 is the same as that of the electrodefingers of the first overlapping region 104. The metallization ratio isdefined as the electrode finger width/(the electrode finger width +thespace between the electrode fingers). As discussed above, in oneexample, the electrode finger pitch of the second overlapping region 105is configured to be greater than that of the first overlapping region.Accordingly, the width of the electrode fingers in the secondoverlapping region 105 is greater than the width of the electrodefingers in the first overlapping region 104. As shown in FIG. 3, in theconventional elastic wave resonator, greater spuriousness 301 occurs onthe lower side of the antiresonant frequency in the transmissioncharacteristic of the conventional elastic wave resonator. In contrast,as shown in FIG. 2, examples of the elastic wave resonator 100 accordingto embodiments of the present invention can suppress spuriousness. Thesuppression of spuriousness can be attributed to the configuration inwhich the frequency of an elastic wave excited in the second overlappingregion 105 is lower than the frequency of an elastic wave excited in thefirst overlapping region 104, achieved by increasing the electrodefinger pitch of the second overlapping region 105 in comparison with theelectrode finger pitch of the first overlapping region 104.

As discussed above, embodiments of the elastic wave resonator accordingto aspects of the present invention can suppress spuriousness in thetransmission characteristic of the elastic wave resonator such that adownsized elastic wave resonator having improved characteristics can berealized.

Certain embodiments of the elastic wave resonator 100 are configured toeliminate dummy electrode fingers (electrode fingers that do not extendto the second overlapping region 105) in the dummy region 107 of thecomb-shaped electrode 102. However, other embodiments can usecomb-shaped electrodes 402 provided with such dummy electrode fingers,as shown in FIG. 4, for example

In addition, although in certain embodiments the electrode finger pitchis greatest in the second overlapping region 105, in other examples,comb-shaped electrodes 502 and reflector electrodes 503 can be used inwhich the electrode finger pitch is greatest in the dummy region 501. Anexample of this configuration is illustrated in FIG. 5. In this example,the propagation direction length of the busbar electrode 510 connectedto the electrode fingers of the comb-shaped electrode 502 is greaterthan the propagation direction length (L) of the first overlappingregion 104 of the comb-shaped electrode 502. This configuration caneliminate the second connection electrode fingers 108, which may allowthe overlapping width to be reduced.

Furthermore, similar effects can be achieved using other configurationsof the comb-shaped electrodes 102, 502, such as those illustrated inFIGS. 6 and 7, for example. Still further, similar effects can beachieved in a longitudinal-mode-type elastic surface wave filter inwhich a plurality of comb-shaped electrodes (i.e., including comb-shapedelectrodes similar to any of the comb-shaped electrodes 102, 402, 502,etc.) are adjacently arranged in the propagation direction of an elasticwave.

As discussed above, in certain examples a Y-cut 128-degree LiNbO₃substrate is used for the piezoelectric substrate of the elastic wavefilter; however, embodiments of the elastic wave resonator are notlimited in this regard, and other piezoelectric substrates can be used.For example, suppression of spuriousness in the transverse mode can beachieved by embodiments of the elastic wave filter of FIG. 1 using aLiNbO₃ substrate wherein the cut angle ranges from 120 degrees to 135degrees in Y-cut, such that an elastic wave resonator having improvedcharacteristics can be realized.

In addition, the material of the electrodes is not limited to thespecific examples disclosed herein, and a layered structure of highdensity electrodes with Aluminum-based materials, or a single layerelectrode can be implemented.

Furthermore, the number of the comb-shaped electrodes and reflectorelectrodes and the electrode finger pitch are not limited to thespecific examples disclosed herein. Although certain embodiments includesecond overlapping regions 105 that are the same and provided on bothsides in the overlapping width direction of the first overlapping region104, in other examples, the second overlapping regions 105 differ fromone another. Similar effects can be achieved at least by a configurationin which the frequency of an elastic wave excited by the secondoverlapping regions 105 is lowered in comparison with that of an elasticwave excited by the first overlapping region 104.

As discussed above, in certain examples the elastic wave resonator 100is configured such that the electrode finger pitch of the secondoverlapping region 105 is greater than the electrode finger pitch of thefirst overlapping region 104 throughout the whole region of thecomb-shaped electrode in the propagation direction of an elastic wave.However, other embodiments can have different configurations, and thespecific examples disclosed herein are not intended to be limiting. Forexample, the electrode finger pitch of the second overlapping region 105can be the same as or less than the electrode finger pitch of the firstoverlapping region 104 around both edges of the comb-shaped electrode inthe propagation direction of an elastic wave (in portions adjacent tothe reflectors 103). Thus, even though the magnitude relationship variesbetween the electrode finger pitches in a portion of the comb-shapedelectrode, the effects discussed above can be achieved provided that thefrequency of an elastic wave excited by the second overlapping region105 is lower than the frequency of an elastic wave excited by the firstoverlapping region 104. Similarly, a portion lacking the secondoverlapping region can be included in a portion of the comb-shapedelectrode.

Although in some examples the metallization ratios are the same betweenthe first overlapping region 104 and the second overlapping region 105,in other examples the metallization ratios can be different. A similareffect can be obtained provided that the frequency of an elastic wave inthe second overlapping region 105 is lower than the frequency of anelastic wave in the first overlapping region 104.

It will be appreciated by those skilled in the art, given the benefit ofthis disclosure, that configuring a filter and an antenna duplexer touse embodiments of the elastic wave resonator 100 according to thisdisclosure can realize a filter and/or an antenna duplexer having lessspuriousness in the transverse mode and improved characteristics, aswell as a module and a communication device having enhanced performanceusing the same, as discussed further below.

Referring to FIG. 8, there is illustrated another embodiment of anelastic wave resonator 800. As shown in FIG. 8, the configuration ofthis example includes first phase region electrode fingers 809 andsecond phase region electrode fingers 811, the phase of an elastic wavegenerated by the first phase region electrode fingers 809 beingdifferent from the phase of an elastic wave generated by the secondphase region electrode fingers 811. In this example, the electrodefingers of the first overlapping region 804 connected to the first phaseregion electrode fingers 809 have a 180-degree difference relationshipwith the electrode fingers of the first overlapping region 804 connectedto the second phase region electrode fingers 811. As a result, the phaseof an elastic wave in the first phase region is different from the phaseof an elastic wave in the second phase region. In one example, in orderto realize the configuration, the first and the second connectionelectrode fingers 806, 808 are connected in a direction opposite andoblique with each other to the first and the second phase regionelectrode fingers 809, 811.

FIG. 9 shows a transmission characteristic for one example of theelastic wave resonator 800 of FIG. 8. For comparison, FIG. 10 shows atransmission characteristic according to the conventional elastic waveresonator of FIG. 19. In the example corresponding to FIG. 9, a128-degree LiNbO₃ substrate is used for the piezoelectric substrate sothat a Rayleigh wave is the primary elastic wave. In this example, theelectrode finger pitch of the first overlapping region 804 is 2.00 μm,and the electrode finger pitch of the second overlapping region 805 is2.02 μm. Additionally, the number of the electrode fingers of thecomb-shaped electrode is two hundred (200), and the number of theelectrode fingers of the reflector is thirty (30). As shown in FIG. 10,greater spuriousness 1001 occurs on the lower side of the anti-resonantfrequency in the transmission characteristic of the conventional elasticwave resonator. In contrast, as shown in FIG. 9, embodiments of theelastic wave resonator 800 according to aspects of the present inventioncan suppress the spuriousness. The suppression of the spuriousness canbe attributed to the configuration in which the frequency of an elasticwave excited in the second overlapping region 805 is lower than thefrequency of an elastic wave excited in the first overlapping region804, achieved, for example, by increasing the electrode finger pitch ofthe second overlapping region 805 in comparison with the electrodefinger pitch of the first overlapping region 804.

As discussed above, embodiments of the elastic wave resonator 800 cansuppress spuriousness in the transmission characteristic of the elasticwave resonator so that an improved elastic wave resonator can berealized. Furthermore, configuring the comb-shaped electrode 802 to havethe number of the electric fingers in the second overlapping region 805be less than that of the first overlapping region 804 can preventdefectively formed electrodes caused by the first and the secondconnection electrodes 807, 808 being too thin to perform sufficientexposure, etching and the like.

In addition, as shown in FIG. 11, in certain examples, the comb-shapedelectrode 802 and the reflector electrodes 803 may be covered with adielectric thin film 1101. FIG. 12 shows a transmission characteristicof an example of the elastic wave resonator when a SiO₂ thin film isused for the dielectric thin film 1101. The thickness of the SiO₂ thinfilm can be approximately 33% of the normalized wavelength. Forcomparison, FIG. 13 shows a transmission characteristic for an examplein which the comb-shaped electrodes and the reflector electrodes of aconventional elastic wave resonator are covered with a SiO₂ thin film.As shown in FIG. 13, greater spuriousness 1301 occurs on the lower sideof the anti-resonant frequency in the transmission characteristic of theconventional elastic wave resonator. In contrast, as shown in FIG. 12,embodiments of the elastic wave resonator 800 according to aspects ofthe present invention can suppress the spuriousness even when thecoating of a SiO₂ thin film exists. Further, the elastic wave resonator800 according to embodiments disclosed herein can improve thetemperature characteristic of the elastic wave resonator, and devicesincluding such elastic wave resonators with the SiO₂ thin film.

Certain embodiments of the elastic wave resonator 800 are configured toeliminate dummy electrode fingers in the dummy region 807 of thecomb-shaped electrode 802. However, other embodiments can usecomb-shaped electrodes 402 provided with such dummy electrode fingers,similar to the example as shown in FIG. 4.

In addition, although in certain examples, the electrode finger pitch isgreatest in the second overlapping region 805; other examples can usecomb-shaped electrodes 1402 and reflector electrodes 1403 in which theelectrode finger pitch is greater in the dummy region 1401, as shown inFIG. 14, for example. In this case, the propagation direction length ofthe busbar electrode 1410 connected to the electrode fingers of thecomb-shaped electrode 1402 is greater than the propagation directionlength of the first overlapping region 804 of the comb-shaped electrode1402. This configuration can eliminate the second connection electrodefingers 808 and therefore the overlapping width can be reduced.

As discussed above, the effect of reduced spuriousness and otheradvantages can be achieved using a variety of configurations of thecomb-shaped electrodes 102, 402, 502, 802, 1402. Still further, similareffects can be achieved in a longitudinal-mode-type elastic surface wavefilter in which a plurality of comb-shaped electrodes 102, 402, 502,802, 1402 are adjacently arranged in the propagation direction of anelastic wave.

As discussed above, in certain examples a Y-cut 128-degree LiNbO₃substrate is used for the piezoelectric substrate of the elastic wavefilter; however, embodiments of the elastic wave resonator are notlimited in this regard, and other piezoelectric substrates can be used.For example, suppression of spuriousness in the transverse mode can beachieved by embodiments of the elastic wave filter of FIG. 8 using aLiNbO₃ substrate wherein the cut angle ranges from 120 degrees to 135degrees in Y-cut, such that an elastic wave resonator having an improvedcharacteristic can be realized.

In addition, the material of the electrodes is not limited to thespecific examples disclosed herein, and a layered structure of highdensity electrodes with Aluminum-based materials, or a single layerelectrode can be implemented.

In addition, the number of the comb-shaped electrodes and reflectorelectrodes and the electrode finger pitch are not limited to thespecific example of FIG. 8. Although the second overlapping regions 805provided on both sides in the overlapping width direction of the firstoverlapping region 804 are the same in some examples, the secondoverlapping regions 805 can be different in other examples. The similareffect can be achieved at least by configurations in which the frequencyof an elastic wave excited by the second overlapping regions 805 islower in comparison with that of an elastic wave excited by the firstoverlapping region.

Furthermore, the thickness of SiO₂ layer is not limited to this specificexample and can be optimized according to the acoustic velocity of theprimary elastic wave, other spuriousness, the cut angle, and the like.Still further, a similar effect can be achieved in embodiments of theelastic wave filter of FIG. 1 when a coating of the SiO₂ thin film isincluded.

It will be appreciated by those skilled in the art, given the benefit ofthis disclosure, that configuring a filter and an antenna duplexer touse embodiments of the elastic wave resonator 800 according to thisdisclosure can realize a filter and/or an antenna duplexer having lessspuriousness in the transverse mode and improved characteristics, aswell as a module and/or a communication device having enhancedperformance using the same.

As discussed above, embodiments of the elastic wave resonator accordingto aspects of the present invention can achieve the effect of realizingan elastic wave resonator having less spuriousness and improvedcharacteristics. Furthermore, configuring an elastic wave filter to usesuch an elastic wave resonator can achieve the effect of realizing anelastic wave filter having improved characteristics. FIG. 15 illustratesan example of a ladder-type elastic wave filter 1500 in whichembodiments of the elastic wave resonator 100 and/or 800 may be used.The elastic wave filter 1500 includes one or more series arm resonators1505 a and one or more parallel arm resonators 1505 b. In the exampleillustrated in FIG. 15, the elastic wave filter 1500 includes threeseries arm resonators 1505 a and two parallel arm resonators 1505 b;however, it is to be appreciated that embodiments of the elastic wavefilter are not so limited and may include any number of series arm andparallel arm resonators. The series arm resonators 1505 a are connectedin series along a signal path between a first terminal 1501 and a secondterminal 1503. The parallel arm resonators 1505 b are connected betweenthe signal path and a ground 1507. Any one or more of the series armresonators 1505 a and/or parallel arm resonators 1505 b can be anembodiment of the elastic wave resonators 100 or 800 discussed above.Embodiments of the elastic wave resonators 100 and 800 can suppressspuriousness in the transmission characteristic of the elastic waveresonator, such that a downsized elastic wave resonator having improvedcharacteristics can be realized. Embodiments of the elastic waveresonator 800 may also have an improved temperature characteristic.Accordingly, incorporation of one or more of these elastic waveresonators 100, 800 into the elastic wave filter 1500 can provide afilter having improved characteristics, such as smaller size, improvedtransmission characteristics (including reduced spuriousness), andimproved temperature stability or performance, for example.

According to one embodiment, the elastic wave filter 1500 may be used toprovide an antenna duplexer having improved characteristics. FIG. 16illustrates a block diagram of one example of an antenna duplexer whichmay incorporate embodiments of the elastic wave filter 1500, andtherefore embodiments of the elastic wave resonators 100 and/or 800. Theantenna duplexer 1600 includes a transmission filter 1610 and areception filter 1620 that are connected to a shared antenna terminal1630. The transmission filter 1610 includes a transmission-side terminal1615 for connecting the transmission filter to transmitter circuitry,and the reception filter includes a receive-side terminal 1625 forconnecting the reception filter to receiver circuitry. Either or both ofthe transmission filter 1610 and the reception filter 1620 can be anembodiment of the elastic wave filter 1500. In an example in which theelastic wave filter 1500 is used as the transmission filter 1610, thefirst terminal 1501 of the elastic wave filter 1500 may correspond tothe transmission-side terminal 1615, and the second terminal 1503 of theelastic wave resonator 1500 may correspond to the antenna terminal 1630.Similarly, in an example in which the elastic wave filter 1500 is usedas the reception filter 1610, the first terminal 1501 of the elasticwave filter 1500 may correspond to the antenna terminal 1630, and thesecond terminal 1503 of the elastic wave resonator 1500 may correspondto the receive-side terminal 1625. By configuring the antenna duplexer1600 to use the elastic wave filter 1500, which includes one or more ofthe elastic wave resonators 100 and/or 800, an antenna duplexer havingimproved characteristics and enhanced performance (resulting from theimproved characteristics of the elastic wave resonators 100, 800discussed above) can be realized.

As discussed above, embodiments of the elastic wave resonators 100, 800may be incorporated, optionally as part of an elastic wave filter 1500and/or antenna duplexer 1600, into a module that may ultimately be usedin a device, such as a wireless communications device, for example, soas to provide a module having enhanced performance. FIG. 17 is a blockdiagram illustrating one example of a filter module 1700 including theelastic wave filter 1500 of FIG. 15. The module 1700 further includesconnectivity 1710 to provide signal interconnections, packaging 1720,such as for example, a package substrate, for packaging of thecircuitry, and other circuitry die 1730, such as, for exampleamplifiers, pre-filters, modulators, demodulators, down converters, andthe like, as would be known to one of skill in the art of semiconductorfabrication in view of the disclosure herein. In certain embodiments,the elastic wave filter 1500 in module 1700 may be replaced with theantenna duplexer 1600, so as to provide an RF module, for example.

Furthermore, configuring an elastic wave filter and an/or antennaduplexer to use embodiments of the elastic wave resonator 100 and/or 800can achieve the effect of realizing a communication device havingenhanced performance using the same. FIG. 18 is a schematic blockdiagram of one example of a communication device 1800 (e.g., a wirelessor mobile device) that can include the antenna duplexer 1600incorporating one or more elastic wave resonators 100, 800, as discussedabove. The communication device 1800 can represent a multi-band and/ormulti-mode device such as a multi-band/multi-mode mobile phone, forexample. In certain embodiments, the communication device 1800 caninclude the antenna duplexer 1600, a transmission circuit 1810 connectedto the antenna duplexer via the transmission-side terminal 1615, areception circuit 1820 connected to the antenna duplexer 1600 via thereceive-side terminal 1625, and an antenna 1830 connected to the antennaduplexer via the antenna terminal 1630. The transmission circuit 1810and reception circuit 1820 may be part of a transceiver that cangenerate RF signals for transmission via the antenna 1830 and canreceive incoming RF signals from the antenna 1830. The communicationdevice 1800 can further include a controller 1840, a computer readablemedium 1850, a processor 1860, and a battery 1870.

It will be understood that various functionalities associated with thetransmission and receiving of RF signals can be achieved by one or morecomponents that are represented in FIG. 18 as the transmission circuit1810 and the reception circuit 1820. For example, a single component canbe configured to provide both transmitting and receivingfunctionalities. In another example, transmitting and receivingfunctionalities can be provided by separate components.

Similarly, it will be understood that various antenna functionalitiesassociated with the transmission and receiving of RF signals can beachieved by one or more components that are collectively represented inFIG. 18 as the antenna 1830. For example, a single antenna can beconfigured to provide both transmitting and receiving functionalities.In another example, transmitting and receiving functionalities can beprovided by separate antennas. In yet another example in which thecommunication device is a multi-band device, different bands associatedwith the communication device 1800 can be provided with differentantennas.

To facilitate switching between receive and transmit paths, the antennaduplexer 1600 can be configured to electrically connect the antenna 1830to a selected transmit or receive path. Thus, the antenna duplexer 1600can provide a number of switching functionalities associated with anoperation of the communication device 1800. In addition, as discussedabove, the antenna duplexer 1600 includes the transmission filter 1610and reception filter 1620, which are configured to provide filtering ofthe RF signals As discussed above, either or both of the transmissionfilter 1610 and reception filter 1620 can include embodiments of theelastic wave filter 1500 including one or more elastic wave resonators100 and/or 800, and thereby provide enhanced performance through thebenefits of reduced spuriousness and improved characteristics achievedusing embodiments of the elastic wave resonators 100 and/or 800.

As shown in FIG. 18, in certain embodiments, a controller 1840 can beprovided for controlling various functionalities associated withoperations of the antenna duplexer 1600 and/or other operatingcomponent(s). In certain embodiments, a processor 1860 can be configuredto facilitate implementation of various processes for operation of thecommunication device 1800. The processes performed by the processor 1860may be implemented by computer program instructions. These computerprogram instructions may be provided to a processor of a general purposecomputer, special purpose computer, or other programmable dataprocessing apparatus to produce a machine, such that the instructions,which execute via the processor of the computer or other programmabledata processing apparatus, create a mechanism for operating thecommunication device 1800. In certain embodiments, these computerprogram instructions may also be stored in the computer-readable medium1850. The battery 1870 can be any suitable battery for use in thecommunication device 1800, including, for example, a lithium-ionbattery.

Having described above several aspects of at least one embodiment, it isto be appreciated various alterations, modifications, and improvementswill readily occur to those skilled in the art. Such alterations,modifications, and improvements are intended to be part of thisdisclosure and are intended to be within the scope of the invention.Accordingly, the foregoing description and drawings are by way ofexample only, and the scope of the invention should be determined fromproper construction of the appended claims, and their equivalents.

What is claimed is:
 1. An elastic wave resonator comprising: apiezoelectric substrate; a pair of comb-shaped electrodes provided on asurface of the piezoelectric substrate, the pair of comb-shapedelectrodes including first and second overlapping regions in whichelectrode fingers of the comb-shaped electrodes interdigitate, thesecond overlapping region being provided on both outside edges of thefirst overlapping region in an overlapping width direction, anoverlapping width of the first overlapping region being greater than anoverlapping width of the second overlapping region, the pair ofcomb-shaped electrodes being configured to excite a first elastic wavein the first overlapping region and to excite a second elastic wave inthe second overlapping region, a frequency of the first elastic wavebeing higher than a frequency of the second elastic wave; and a pair ofreflectors disposed on the surface of the piezoelectric substrateopposing one another on opposite sides of the pair of comb-shapedelectrodes along a propagation direction of the first and second elasticwaves.
 2. The elastic wave resonator of claim 1 wherein an electrodefinger pitch in the second overlapping region is greater than anelectrode finger pitch in the first overlapping region.
 3. The elasticwave resonator of claim 1 wherein the first overlapping region includesa first number of electrode fingers, and the second overlapping regionincludes a second number of electrode fingers fewer than the firstnumber of electrode fingers.
 4. The elastic wave resonator of claim 1wherein the electrode fingers in the first overlapping region and theelectrode fingers in the second overlapping region are connected viafirst connection electrode fingers, the first connection electrodefingers extending obliquely in a first direction relative to a seconddirection in which the electrode fingers extend in the first overlappingregion.
 5. The elastic wave resonator of claim 4 wherein the pair ofcomb-shaped electrodes further includes a dummy region in which theelectrode fingers of the pair of comb-shaped electrodes do not overlapwith each other.
 6. The elastic wave resonator of claim 5 wherein theelectrode fingers in the second overlapping region and the electrodefingers in the dummy region are connected via second connectionelectrode fingers, the second connection electrode fingers extendingobliquely in a third direction relative to the second direction, thethird direction being opposite to the first direction.
 7. The elasticwave resonator of claim 6 wherein an electrode finger pitch in the dummyregion is greater than an electrode finger pitch in the firstoverlapping region.
 8. The elastic wave resonator of claim 7 wherein theelectrode fingers of the pair of comb-shaped electrodes are connected toa busbar electrode having a length in the propagation direction that isgreater than a length in the propagation direction of the firstoverlapping region.
 9. The elastic wave resonator of claim 1 wherein awidth of the electrode fingers in the second overlapping region isgreater than a width of the electrode fingers in the first overlappingregion.
 10. The elastic wave resonator of claim 1 wherein thepiezoelectric substrate is made of lithium niobate and has a cut angleranging from 120 degrees to 135 degrees in Y-cut.
 11. The elastic waveresonator of claim 1 further comprising a dielectric thin film made ofSiO₂ disposed over the pair of comb-shaped electrodes.
 12. The elasticwave resonator of claim 1 wherein the second overlapping region includesa first phase region and a second phase region, a phase of the secondelastic wave excited by the electrode fingers in the first phase regionbeing different from a phase of the second elastic wave generated by theelectrode fingers in the second phase region.
 13. An elastic wave filtercomprising: a piezoelectric substrate; and a plurality elastic waveresonators disposed on a surface of the piezoelectric substrate, eachelastic wave resonator including a pair of comb-shaped electrodes havingfirst and second overlapping regions in which electrode fingers of thecomb-shaped electrodes interdigitate, the second overlapping regionbeing provided on both outside edges of the first overlapping region inan overlapping width direction, an overlapping width of the firstoverlapping region being greater than an overlapping width of the secondoverlapping region, an electrode finger pitch in the second overlappingregion being greater than an electrode finger pitch in the firstoverlapping region, and the pair of comb-shaped electrodes beingconfigured to excite a first elastic wave in the first overlappingregion and to excite a second elastic wave in the second overlappingregion, a frequency of the first elastic wave being higher than afrequency of the second elastic wave.
 14. The elastic wave filter ofclaim 13 wherein each of the plurality of elastic wave resonatorsfurther includes a dielectric film made of SiO₂ disposed over the pairof comb-shaped electrodes.
 15. The elastic wave filter of claim 13wherein the elastic wave filter has a ladder-type configuration, theplurality of elastic wave resonators including a plurality of series-armresonators connected in series along a signal path extending between aninput of the elastic wave filter and an output of the elastic wavefilter, and a plurality of parallel-arm resonators connected between thesignal path and ground.
 16. The elastic wave filter of claim 13 whereinthe first overlapping region includes a first number of electrodefingers, and the second overlapping region includes a second number ofelectrode fingers fewer than the first number of electrode fingers. 17.The elastic wave filter of claim 13 wherein the electrode fingers in thefirst overlapping region and the electrode fingers in the secondoverlapping region are connected via first connection electrode fingers,the first connection electrode fingers extending obliquely in a firstdirection relative to a second direction in which the electrode fingersextend in the first overlapping region.
 18. The elastic wave filter ofclaim 17 wherein the pair of comb-shaped electrodes further includes adummy region in which the electrode fingers of the pair of comb-shapedelectrodes do not overlap with each other, the electrode fingers in thesecond overlapping region and the electrode fingers in the dummy regionbeing connected via second connection electrode fingers, the secondconnection electrode fingers extending obliquely in a third directionrelative to the second direction, the third direction being opposite tothe first direction.
 19. The elastic wave filter of claim 18 wherein anelectrode finger pitch in the dummy region is greater than the electrodefinger pitch in the first overlapping region.
 20. An elastic waveresonator comprising: a piezoelectric substrate; and a pair ofcomb-shaped electrodes provided on a surface of the piezoelectricsubstrate, the pair of comb-shaped electrodes including first and secondoverlapping regions in which electrode fingers of the comb-shapedelectrodes interdigitate, the second overlapping region being providedon both outside edges of the first overlapping region in an overlappingwidth direction, an overlapping width of the first overlapping regionbeing greater than an overlapping width of the second overlappingregion, the pair of comb-shaped electrodes being configured to excite afirst elastic wave in the first overlapping region and to excite asecond elastic wave in the second overlapping region, a frequency of thefirst elastic wave being higher than a frequency of the second elasticwave, the first overlapping region including a first number of electrodefingers, and the second overlapping region including a second number ofelectrode fingers fewer than the first number of electrode fingers, andthe second overlapping region including a first phase region and asecond phase region, a phase of the second elastic wave generated by theelectrode fingers in the first phase region being different from a phaseof the second elastic wave generated by the electrode fingers in thesecond phase region.